I was asked to repost this thread, so here it is. New findings from this leak are still being posted regularly, but here's the story so far:
Kishi said:Earlier today, hobbyists obtained a large volume of Nintendo's old files, including early builds of Super NES games as well as source code for existing games (listed below).
The full extent of the knowledge to be gained here is still unknown as people in the community continue to analyze all this suddenly-unearthed data, but here are some highlights:
Super Mario World
↑ Unused sprites of the Super Leaf power-up from Super Mario Bros. 3 (known to have been in the game at one point due to ancient magazine scans).
↑ A skydiving helmet for Mario.
↑ More frames for Tail Mario, small Mario sprites resembles those used in the Super NES Test Program, the Venus Fire Trap from SMB3, and an early face for Wiggler.
↑ Early Blargg concepts (much larger than the final version) and dolphin designs. You can see several works in progress, with only partial outlines.
↑ Now the earliest known design of Yoshi (not counting Miyamoto's pencil sketch), who went through several forms during development.
↑ Unused graphics for Bowser, including a frame outside the Koopa Clown. The Koopa Clown also seemed to have a turn-key in place of its propeller, and there's an odd, smaller enemy resembling a Piranha Plant with eyes.
↑ Early sprites for Peach (some clearly placeholder) and a frame of Mario without his hat.
↑ An early world map design. The Piranha Plant still exists in the final ROM.
↑ A grandfatherly Yoshi with a beard and cane.
The Legend of Zelda: A Link to the Past
↑ Early sprites for Link.
↑ Side-view sprites of Link, all of which appear suited to some kind of battle scene.
Super Mario Kart
↑ A detailed animation for being flattened by a Thwomp. Even more interestingly, the character appears to be a car with eyes, potentially implying the game was in development before Mario was attached.
↑ An early map screen.
↑ Early gameplay.
↑ An early world map design.
↑ Apparently an early design for Burt.
↑ An early, work-in-progress frame for the final battle against the gigantic Baby Bowser.
→ An early build with a more animated stage select screen, early UI elements (particularly for throwing eggs), and the subtitle Super Mario Bros. 5.
→ An unused mini-game where Baby Mario hands Yoshi bombs to drop on houses.
Super Donkey Kong
↑ A barely-playable prototype ROM labeled "super donkey," as in Super Donkey Kong, the Japanese title of Donkey Kong Country. The art style is a perfect match for Yoshi's Island, and it features similar mechanics such as the ground pound, but the player character is an unfamiliar human. This seems to point to a different game—whether it be the original vision for DKC before Rare came on, an actual late SNES Mario game ("Super Mario Bros. 5"), a combination of the two, or something else entirely—being prototyped, cancelled, and heavily reworked into what we know today as Yoshi's Island.
↑ Donkey Kong.
Star Fox 2
↑ An early map screen—apparently earlier than a similar one shown to the press during the game's development. Placeholder graphics of a Blooper and a Ghini from Link's Awakening are in place.
↑ An unnamed sheep character in place of Fay the dog. This character had previously been seen only on a provisional title screen in the pages of Nintendo Power, where her face had been obscured by the build date.
↑ Earlier portrait designs for Fox, Falco, and the sheep, as well as a human pilot.
Also included in the leak are pre-release builds of a number of third-party games released between 1991 and '92. These appear to feature more minor differences from their final versions, but again, new discoveries are being made even now. And while some answer long-standing questions, others are raising new ones as the mystery continues to unfold.
narcodis said:Dylan Cuthbert chimed in on some of the stuff that got leaked:
RT-55J said:The music in the Super Donkey video was apparently added by the author in post, and not part of the game.
Also, it looks like those first two Star Fox pictures are probably from a an early prototype of Star Fox 1, not 2. Barrel rolling isn't implemented, and there apparently aren't any character graphics the ROM. I wouldn't be surprised if it was from the point when the project was still a Starglider sequel.
The music slaps tho:
Keurig said:Phantoon said:I'm wondering if the character in Super Donkey is Stanley the Bugman from Donkey Kong III. He gets a weird projectile weapon that reminds me of that game.
I also wonder if this got repurposed because Rare chose to do a Donkey Kong game. In which case we'd never have got Yoshi's Island...
Looks like the main character might have intended to have been Mario at one point:
Taken from the Era thread
RT-55J said:The training course music in Yoshi's Island was substantially longer:
madhair60 said:The stomp attack in Super Donkey with the two little ghosties flying out ended up in Mario Maker, which is bonkers
The side-view Link sprites apparently went through several revisions:
I like how in the top-down walk cycle in the second file there that you can see Link's nose extend beyond his hair.
Also, I think it's notable just how much of resemblance Link's face here has to his face in Zelda 3's font (on the wanted posters). 
RT-55J said:Super FX Yoshi model:
Starxxon said:It doesn't seem part of a particular game, it was found in a folder with various 3D models experiment (including a swordsman called Link), in the same format as some Star Fox assets.Is this apart of the yoshis island prototypes?
Assets from Dragonfly (Pilotwings beta):
Apparently the project name for F-Zero was CAR RACE. Scintillating. (I haven't seen anybody do a deep dive into it yet.)
Kazin said:According to this thread, at one point the Game Boy Color was going to have a built in tool to let you select the palettes for monochrome Game Boy games, similar (I would guess, anyway) to the Super Game Boy. I always thought it was weird that changing the palettes was a sorta hidden feature and only possible on the boot up screen! I wish they'd have implemented this, so if I forget to change Kirby's Dreamland 2's piss yellow default color scheme, I could correct it without rebooting
Phantoon said:More of the leak has come out, including Mario 64's source code and both N64 Zeldas
RT-55J said:The vast majority of the Zelda 64 (OoT, Master Quest, and MM) source files available are completely empty - 860 out of 894 of them.
RT-55J said:It looks like that tweet was just referring to the code (.c and .h files). Judging by threads such as this, the assets are fine, and there is plenty of beta stuff to sift through.Phantoon said:Nooooooo! That's the one that I think most people would want most. To see the build behind those early screenshots.
He has separate cycles for when he's holding a sword and shield, but I didn't feel like guessing as to how those sprites attach to his hands, heh.
RT-55J said:Big picture dumps of Zelda 3 stuff:
still no SNES F-Zero stuff D:
RT-55J said:Some really rough SGI workstation demos. One might have been a Zelda thing, and the other are definitely racing game tests.
2D art by Tsuyoshi Watanabe for an unidentified project(s), from the period between his work on Zelda 3 ('91) and Star Fox ('93). Definitely Super FX related.
These look like they'd fit in the white squares in the above picture:
These look like Super FX textures:
More textures. The smoke cloud in the top-right here matches the one in Star Fox almost exactly:
Japanese text. I see a number of repeated kanji, so I suspect this is closer to a script than a font (though I don't see much kana, so I'm not sure if it's intelligible). (Note: I can't read Japanese.)
This stuff dates from Dec '91 to Feb '92. My wild guess is that these are early Starglider 3 concepts before the project switched direction to the Star Fox we're familiar with, though this could just as easily be something else entirely (for reference, the Star Fox proto from this leak is from Sept '92).
Kishi said:RT-55J said:Also, it looks like those first two Star Fox pictures are probably from a an early prototype of Star Fox 1, not 2. Barrel rolling isn't implemented, and there apparently aren't any character graphics the ROM. I wouldn't be surprised if it was from the point when the project was still a Starglider sequel.
The music slaps tho:
Just listened to this. It is curious that two tracks are clearly early versions of tracks used in Star Fox 2 (Result at 0:00, and Venom at 0:50), especially since Star Fox 1's composer, Hajime Hirasawa, is not credited on the second game.
It could be chalked up to the cultural trend of Japanese publishers not crediting people who have since left the company, as Hirasawa left Nintendo in 1992—supposedly over disputes regarding ownership of his music, interestingly enough.
Bongo said:They found source code for some NES games, including SMB1. The SMB1 source code had some lines commented out. Someone uncommented them, but in order to get it to run correctly they had to remove some other code in order to free up space. Apparently this behavior for red koopa troopas was removed solely for space limitations:
RT-55J said:Anyhow, it looks like the overworld of Zelda 3 was going to have a more Neutopia-esque art style. It's interesting, but I can see why they decided to change it up.
Also, we have a beta version of Link's Awakening's overworld from back when the scope of the project was just "let's see how much of ALttP we can remake." If you check the other tweets in that thread you can see how some chunks appear to have different (older?) revisions that are more faithful to the source material, possibly indicating that they were in the middle of changing goals when this backup was made.